Effect of Microalloying Ti on Microstructure and Mechanical Properties of Wire and Arc Additively Manufactured Reduced-Activation Ferritic/Martensitic Steel

Wire and arc additive manufacturing (WAAM) is promising for rapid fabrication of the blanket component in fusion plant with a complex embedded inner-channeled structure due to its high forming efficiency and low cost. In this work, a 9Cr reduced-activation ferritic/martensitic steel (RAFMs) thin wall part with inner channels was fabricated by gas metal arc welding technique using optimized process parameters. Flux cored wires were used to adjust the Ti content in each sample. The effect of microalloying Ti on microstructures of as-built RAFMs was studied by optical microscope, electron backscatter diffraction, electron probe microanalysis, scanning electron microscope and transmission electron microscope. It was found that microalloying Ti promoted the formation of martensitic structure and in situ formed TiC and TiO2 particles acted as grain refiners. However, the thermal conductivity of RAFMs decreased with excessive Ti addition, resulting in the formation of coarse ferritic grains with TiC precipitation. The microstructures of each sample were further correlated with their mechanical properties. As-built 0.5Ti-RAFMs exhibited a microhardness of 355 ± 10 HV and ultimate tensile strength values of 840 MPa and 490 MPa at RT and 600 ℃, respectively, which may be used under severe service conditions like those in DEMO